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    SubjectRe: [PATCH] kasan: Always respect CONFIG_KASAN_STACK
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    Hi Nathan,

    Le 14/10/2021 à 18:55, Nathan Chancellor a écrit :
    > On Fri, Oct 08, 2021 at 11:46:55AM -0700, Palmer Dabbelt wrote:
    >> On Thu, 23 Sep 2021 07:59:46 PDT (-0700), nathan@kernel.org wrote:
    >>> On Thu, Sep 23, 2021 at 12:07:17PM +0200, Marco Elver wrote:
    >>>> On Wed, 22 Sept 2021 at 22:55, Nathan Chancellor <nathan@kernel.org> wrote:
    >>>>> Currently, the asan-stack parameter is only passed along if
    >>>>> CFLAGS_KASAN_SHADOW is not empty, which requires KASAN_SHADOW_OFFSET to
    >>>>> be defined in Kconfig so that the value can be checked. In RISC-V's
    >>>>> case, KASAN_SHADOW_OFFSET is not defined in Kconfig, which means that
    >>>>> asan-stack does not get disabled with clang even when CONFIG_KASAN_STACK
    >>>>> is disabled, resulting in large stack warnings with allmodconfig:
    >>>>>
    >>>>> drivers/video/fbdev/omap2/omapfb/displays/panel-lgphilips-lb035q02.c:117:12:
    >>>>> error: stack frame size (14400) exceeds limit (2048) in function
    >>>>> 'lb035q02_connect' [-Werror,-Wframe-larger-than]
    >>>>> static int lb035q02_connect(struct omap_dss_device *dssdev)
    >>>>> ^
    >>>>> 1 error generated.
    >>>>>
    >>>>> Ensure that the value of CONFIG_KASAN_STACK is always passed along to
    >>>>> the compiler so that these warnings do not happen when
    >>>>> CONFIG_KASAN_STACK is disabled.
    >>>>>
    >>>>> Link: https://github.com/ClangBuiltLinux/linux/issues/1453
    >>>>> References: 6baec880d7a5 ("kasan: turn off asan-stack for clang-8 and earlier")
    >>>>> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
    >>>>
    >>>> Reviewed-by: Marco Elver <elver@google.com>
    >>>
    >>> Thanks!
    >>>
    >>>> [ Which tree are you planning to take it through? ]
    >>>
    >>> Gah, I was intending for it to go through -mm, then I cc'd neither
    >>> Andrew nor linux-mm... :/ Andrew, do you want me to resend or can you
    >>> grab it from LKML?
    >>
    >> Acked-by: Palmer Dabbelt <palmerdabbelt@google.com>
    >>
    >> (assuming you still want it through somewhere else)
    >
    > Thanks, it is now in mainline as commit 19532869feb9 ("kasan: always
    > respect CONFIG_KASAN_STACK").
    >
    >>>> Note, arch/riscv/include/asm/kasan.h mentions KASAN_SHADOW_OFFSET in
    >>>> comment (copied from arm64). Did RISC-V just forget to copy over the
    >>>> Kconfig option?
    >>>
    >>> I do see it defined in that file as well but you are right that they did
    >>> not copy the Kconfig logic, even though it was present in the tree when
    >>> RISC-V KASAN was implemented. Perhaps they should so that they get
    >>> access to the other flags in the "else" branch?
    >>
    >> Ya, looks like we just screwed this up. I'm seeing some warnings like
    >>
    >> cc1: warning: ‘-fsanitize=kernel-address’ with stack protection is not supported without ‘-fasan-shadow-offset=’ for this target
    >
    > Hmmm, I thought I did a GCC build with this change but I must not have
    > :/
    >
    >> which is how I ended up here, I'm assuming that's what you're talking about
    >> here? LMK if you were planning on sending along a fix or if you want me to
    >> go figure it out.
    >
    > I took a look at moving the logic into Kconfig like arm64 before sending
    > this change and I did not really understand it well enough to do so. I
    > think it would be best if you were able to do that so that nothing gets
    > messed up.
    >

    I'll do it tomorrow, I'm the last one who touched kasan on riscv :)

    Thanks,

    Alex

    > Cheers,
    > Nathan
    >
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    > linux-riscv@lists.infradead.org
    > http://lists.infradead.org/mailman/listinfo/linux-riscv
    >

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